Method for establishing a communication connection in a direct communication network

ABSTRACT

A method for establishing a communication connection between two subscribers of a plurality of subscribers in a direct communication network is provided. Subscriber address information required for establishing paired communication connections between the subscribers is stored in the plurality of subscribers in a distributed manner; a searching subscriber sends a broadcast request message aimed at the establishment of at least one communication connection between a calling subscriber and at least one sought subscriber; each subscriber receiving the broadcast request message sends a response message containing subscriber address information required for the at least one communication connection, provided that the emission of a response message is associated therewith according to the respective functionality thereof; and said subscriber address information is then used to establish the communication connection between the calling subscriber and the at least one sought subscriber.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2004/009108, filed Aug. 13, 2004 and claims the benefitthereof. The International Application claims the benefits of Germanapplication No. 10345051.3 DE filed Sep. 26, 2003, both of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a method for setting up a communication linkbetween two clients from a plurality of clients in a directlycommunicating communication network.

BACKGROUND OF INVENTION

Communication networks whose components communicate with one another ona packet-switched basis are replacing circuit-switched communicationnetworks to an increased extent. Such directly communicating networksare frequently also called Voice-Over-IP (VoIP) networks if the Internetprotocol (IP protocol) is used for interchanging the audio informationwhich is present in the form of data (voice data). In this case, thenetworks may be used either exclusively for transmitting voice data orelse can transmit both voice data and other information (e.g. data,video) as a mixture.

In circuit-switched communication networks, terminals (e.g. telephones,fax machines) are always connected to a communication node (e.g. atelephone exchange). In this case, any flow of information to and fromthe terminals involves the respective communication node, with controlinformation for setting up connections, for example, being interchangedbetween the terminal and the communication node while, although theuseful information (the analog voice signal or the modulated fax signal)is interchanged between the terminals involved in the communicationlink, it is forwarded (transmitted) by at least one communication nodeinvolved in the communication link.

In voice data networks, the terminals are frequently called “clients”,because the terminals in these communication networks are operated in asimilar manner to a computer in a data network and may be in the formnot only of a telephone or a fax machine, but also of a multimedia PC,for example. The latter terminals are computers which have suitablehardware for inputting information (e.g. a microphone, a camera, akeyboard, a scanner etc.) and outputting information (e.g. ascreen/display, loudspeakers, LEDs etc.). Clients may also be in theform of a miniature PC (a “PDA”—Personal Digital Assistant) or in theform of an added-feature mobile telephone (“smart phone”). Saidappliances are often equipped with a wireless data link and are then, inthe case of mobile telephones, also called “WLAN mobile phones”(WLAN=Wireless Local Area Network).

The clients in the voice data networks usually interchange the usefulinformation with one another directly. To this end, after acommunication link has been set up, two clients communicating with oneanother respectively know the network address of their communicationpartner, and they use these network addresses to interchange the datapackets containing the useful information with one another. To set up aconnection, on the other hand, central network nodes (communicationnodes) are also used in most known voice data networks. Such networknodes are known as “gatekeepers” to the voice data networks using theH.323 protocol (ITU-T-H.323) and as SIP proxy servers in the voice datanetworks using the SIP protocol (IETF-SIP; SIP=Session InitiationProtocol).

In widely ramified data networks, particularly on the Internet,communication structures called “Peer-to-Peer” networks or else“End-To-End” networks are increasingly being used. A primary area ofapplication for such communication structures is the interchange offiles, known as “filesharing”. For this, a subscriber (client) in such acommunication structure interrogates a number of other clients(typically computers) on the search for a particular resource (which maybe a music file or a computer program) and, when this resource has beenfound, starts to use this resource, which usually involves thetransmission (“download”) of a file or a plurality of files. In thiscase, appropriate communication partners (clients) can either be foundusing a database, or else the clients can be found by appropriatecommunication methods automatically, i.e. without a central entity.

Some of the known “Peer-To-Peer” networks are used for the purposes ofdirect communication. The “media data”, that is to say the useful data,interchanged in the process are not limited to voice (voice data) ormodulated information (e.g. fax transmissions), but rather also includemoving-picture information (video transmission, video conferencing,“multimedia messaging”) and other forms of electronic communication too.In such communication networks, which are also called “directlycommunicating communication networks”, it is thus firstly possible toimplement communication links in the style of conventional “telephonecalls”, and it is secondly possible to transmit expanded contents(multimedia) too. In this case, dispensing with central network nodes(communication nodes) has the advantage of increased failsafety, whichhas the associated drawback that the (switching) functionality of thenetwork nodes known from circuit-switched telephony needs to be providedby the clients involved in the communication link themselves.

SUMMARY OF INVENTION

A particular drawback found with the known directly communicatingcommunication networks is that a client needs to have the addressinformation (e.g. the network address) for a second client in order toset up a communication link to the second client. This is a problembecause the client does not normally have a directly associated networknode (e.g. a communication server) from which such an address can berequested. Even if the address information for a required communicationpartner is known, it may occur in directly communicating communicationnetworks that this required communication partner cannot be reached(e.g. if it is “busy” or if the client fails), which means that theconnection needs to be set up to an alternative call destination(“alternate destination”), for example. Since directly communicatingcommunication networks use no central network nodes for storing suchaddress information, the problem of addressing also exists forconnection setup to such an alternative call destination.

It is an object of the invention to propose a method which can be usedto ascertain required address information for communication links indirectly communicating communication networks.

First, client address information which is required for setting uppaired communication links between the clients is stored in distributedform in the plurality of clients. A searching client then transmits abroadcast request message aimed at setting up at least one communicationlink between a calling client and at least one sought client.Subsequently, provided that the broadcast request message's respectivefunctionality means that it has the transmission of a response messageassociated with it, which response message comprises a client addressinformation item which is required for the at least one communicationlink, each client receiving the broadcast request message transmits thisresponse message. Finally, this client address information item is usedto set up the communication link between the calling client and the atleast one sought client.

The method steps described above store the client address informationrequired for setting up a communication link in one or more clients inthe communication network. As a result of a plurality of requestmessages being sent, at least one of these further clients is promptedto send back the previously stored client address information to thesearching clients. This means that setup of the communication link isnot dependent on a single client on which a client address informationitem may be stored, but rather setup of a communication link may also beeffected when individual clients are not available.

The method is advantageously refined by the characterizing features ofdependent claims. In this case, features of the dependent claims mayalso be advantageously combined with one another.

The number of response messages returned is minimized by virtue of areceiving client's functionality including signaling the broadcastrequest message on the client and transmitting the response message whenthe broadcast is taken. This means that firstly signaling is performedonly for such clients as receive the broadcast request message andobtain a positive result when evaluating this broadcast request message,and secondly a response message is transmitted only if the call is to betaken on the respective client.

If a call diversion in cases in which the signaling information sentfrom the calling client to a called client in order to set up a firstcommunication link is rejected or not promptly answered by the calledclient is made by virtue of one of the stored client address informationitems in step a) relating to a call diversion destination client for thecalled client, the request message in step b) comprising an identifierfor the called client, and the client address information item containedin the response message in step c) describing the call diversiondestination client, then a call diversion destination can be stored inthe communication network for a client without needing to reserve acentral memory entity for this. In this case, it is advantageous if thesearching client is formed by the calling client, because in such casesthe calling client receives the response message with the client addressinformation directly without a further intermediate entity and can setup the communication link to the call diversion destination withoutfurther delay. A call diversion destination can be configuredparticularly easily by virtue of a client storing the information thatthis client forms the call diversion destination for another client.Subsequently, the response message is sent by the sought client, whichforms the call diversion destination client, which ensures particularlyfast and safe setup of the communication link.

A call which is waiting on one client can be taken particularly easilyon another client by virtue of a call made by the calling client to thesearching client, which belongs to a call transfer group, beingtransferred by virtue of the client address information in step a)respectively describing the clients associated with the call transfergroup.

If the broadcast request message in step b) is transmitted specificallyto the further clients in the call transfer group which are described inthe client address information, the number of clients addressed in thebroadcast request message is advantageously reduced.

If the communication link in step b) is set up, when there are aplurality of sought clients transmitting the response message, to thatsought client which transmitted the response message first, very rapidconnection setup is achieved. Advantageously, in the course of thecommunication link being set up, a message is sent to the other clientsin the call transfer group which are signaling this call, so that thereis no longer any further signaling in this call, with response messageswhich arrive “late” being rejected.

The clients in the call transfer group which are signaling the call andare not being called directly are prevented from being blocked by virtueof the call signaling in step c) being effected such that the clientsare in a free operating state during the call signaling. Advantageously,this call signaling differs from call signaling for a direct call inwhich the client is already in the “busy” state during call signaling.

A call can be signaled on a plurality of clients simultaneously byvirtue of a group call being made by virtue of the client addressinformation in step a) respectively describing the clients associatedwith the group, and the communication link in step d) being set up tothat sought client transmitting the response message which transmittedthe response message first. In this case, all called clients in thegroup are advantageously in the “busy” state during call signaling.

If the calling client in step c) forms the searching client, the groupmembers to be called can be determined in the calling client directly.

If in step c) an order among the clients assigned to transmit a responsemessage is stipulated in which the call signaling is effected on theseclients in succession, it is possible to implement the known servicefeature of the “cyclic line group”. In this case, it is either possibleto stipulate an order such that the individual clients in the group aresynchronized to one another for the purpose of stipulating the order,alternatively an order can be firmly prescribed, or finally this ordercan also be stipulated afresh with each new call.

By contrast, for setting up a communication link particularly rapidly,it is advantageous if in step c) the call signaling on the clientsassigned to transmit a response message is effected simultaneously. Thecall can then be taken immediately on any affected terminal, with callacceptance on a plurality of clients advantageously involving thecommunication link being set up to that client on which call acceptanceoccurs first, or to that client which has the highest allocatedpriority.

A telephone book (“Directory”) can be created particularly easily in aclient if after step c) the client address information item contained inthe response message is stored by the searching client in an addressdatabase associated with this searching client, and in step d) theaddress database is accessed in order to set up the communication link.Directories with a restricted number of subscribers can be generated byvirtue of the broadcast request message in step b) comprising at leastone filter criterion which is used for selecting particular clients, andthe response message being transmitted in step c) provided that therespective client contains information which meets the at least onefilter criterion and/or the respective client has properties which meetthe at least one filter criterion.

A communication link which is parked on one of the clients in thecommunication network can easily be transferred by another client in thecommunication network by virtue of a communication link to the soughtclient, which is connected to a client used as a waiting destinationwith a waiting destination descriptor, being set up by virtue of thewaiting destination descriptor being sent to the searching client beforestep b), the broadcast request message in step b) comprising the waitingdestination descriptor, the client used as waiting destinationtransmitting the response message in step c), and the connection betweenthe sought client and the client used as waiting destination beingcleared down in step d). This means that any one of a plurality ofclients which are available in the communication network and which canbe used as a waiting destination can be used in order to park acommunication link. The method steps described mean that the client usedas a waiting destination and hence the parked communication link arefound easily and safely without having to define a particular entity ora particular client in the communication network as a waitingdestination permanently.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the inventive method are explained below withreference to the drawings, in which:

FIG. 1 a shows the interchange of messages between clients in a directlycommunicating communication network for the purpose of call diversion ina first variant,

FIG. 1 b shows the interchange of messages between clients for thepurpose of call diversion in a second variant,

FIG. 2 a shows the interchange of messages between clients in order toform a group,

FIG. 2 b shows the interchange of messages between clients for a call toa call transfer group,

FIG. 3 a shows the interchange of messages between clients for a groupcall,

FIG. 3 b shows the interchange of messages between clients for a groupcall in the variant of a cyclic line group,

FIG. 4 shows an arrangement comprising clients in a directlycommunicating communication network, with a subscriber directory beingcreated in one of the clients, and

FIG. 5 shows the interchange of messages between clients for picking upa “parked” communication link.

DETAILED DESCRIPTION OF INVENTION

FIG. 1 a shows the clients A, B, C, which are part of a directlycommunicating communication network (not shown here). The clients A, B,C are “multimedia PCs”, that is to say computers which are connected toa network and which are set up to reproduce and accept audiovisualuseful data. Instead of the multimedia PCs, it is also possible to useother network components which can be used as a communication terminalinstead, for example IP telephones. The clients A, B, C can interchangecontrol data (signaling information) and useful data with one anothervia the directly communicating communication network, which is in theform of a voice data network (VoIP communication network) and whichinterchanges data (voice data, useful data) in line with the Internetprotocol (IP protocol; TCP-IP; UDP-IP).

The arrows shown in FIG. 1 a and in the other figures visualize thetransmission or interchange of messages between the clients which areused to set up a communication link. In this case, the arrows have beenprovided with reference symbols, which can be repeated in the individualfigures, provided that the respective message or control information isa respective message with the same function. Similarly, the clients A,B, C and further clients are shown repeatedly in the figures, providedthat their functionality is not changed between the individual figures.Neither the arrows with the same label nor the clients with the samelabel are described again when they are used repeatedly.

In the communication arrangement shown in FIG. 1 a, the client C isintended to be the call diversion destination for the client B. To setup the call diversion, the user of the client B makes an input in whichclient C is defined as the call diversion destination. On the basis ofthis input, client B sends a control message 11 to client C, with thiscontrol message being taken as a basis for configuring client C as acall diversion destination client for client B (step A). In this case,the control message 11 comprises the descriptor and network address ofclient B as address information. This concludes the configuration of thecall diversion.

Client B now changes to the “offline” operating state; that is to saythat the multimedia PC, which forms client B, is from now on no longerable to be reached in the communication network.

To set up a communication link to client B, client A sends a controlmessage 13 which is addressed to client B and which is intended toprompt call signaling on client B. Since client B can no longer bereached in the communication network, however, no response message issent, which is registered by client A after a waiting time has elapsed(“timeout”).

Alternatively, the case may also arise in which although client B is not“offline” it is not available for setting up the communication link forother reasons. In such cases, client B can receive the control message13 and can respond to it using another control message 14 for rejectingthe call, which means that client A is likewise informed aboutconnection setup to client B not being possible.

To ascertain an alternative call destination for client B, which cannotbe reached, client A sends a broadcast request message to all otherclients which can be reached in the communication network (step B). Sucha broadcast request message which is sent to all the clients which canbe reached is also called a “broadcast message”. Alternatively, such abroadcast request message can also be sent to a restricted number of theclients which can be reached, in which case it is called a “multicastmessage”.

The search message 15 sent as a broadcast request message in the form ofa “broadcast message” is received by all those clients which can bereached in the communication network, FIG. 1 a showing client C by wayof example. When the control message 11 was received, client C storedthe address information of the call diversion destination for client B,it being the network address of client C itself which defines the calldiversion destination for client B. When the search message 15 isreceived, which comprises the address information of client A as sender,client C establishes that this search message 15 relates to client Citself, and as a result client C sends a response message 16 to clientA, which comprises the address information of client C as an indicationof the call diversion destination (step c). In a similar manner to thecontrol message 13 for setting up the communication link to client B,client A now sends a new control message 17 containing signalinginformation to client C, as a result of which the communication linkbetween client A and client C is set up (step d).

FIG. 1 b shows a further exemplary embodiment of call diversion in adirectly communicating communication network, where a further client Dis shown for clients A, B, C from the preceding exemplary embodiment.Like clients A, B, C client D is also in the form of a multimedia PC ina technically similar manner. In this example too, client C is intendedto form the call diversion destination for client B, but with client Bnot being able to set up a direct link to client C at the time at whichthe call diversion is configured. For this reason, client B sends acontrol message 12 (configuration message) to client D, this controlmessage being used to transmit, as address information for the calldiversion destination, the network address of client C and naturally, asinformation about the diverted call destination, the address informationand the name of client B to client D (step a). When this configurationhas taken place, client B is turned off.

To set up a communication link between client A and client B, client Asends a control message 13 to client B, requesting setup of thecommunication link. Since no response comes from client B within thedefined waiting time (in this case too, a negative response 14 isalternatively possible), client A in turn sends a search message 15 to aplurality of clients (step b), this time as a “multicast message” toclients C and D arranged in the communication network. This searchmessage 15 contains a definition that client A is looking for asubstitute call destination for client B. It goes without saying that anaddress information item describing client A is also part of the searchmessage 15. The search message 15 is received by clients C and D, clientD containing a database entry which matches the search query 15. This isbecause in this case the match is established between client B definedin the search message 15 and the call diversion destination configuredin the course of reception of the control message 12. Client B thereforenow sends a response message 18 to client A, transmitting to client Athe information that the call diversion destination for client Bcomprises the address information item associated with client C (stepc). Client A now sends a control message 19 to client C (step d), thiscontrol message 19 using additional information held in the signalinginformation to express that this requested communication link is acommunication link which is diverted for client B. Client C now signalsan incoming call, with a display on the user interface revealing thatthis incoming call is a call which was originally addressed to client B.

FIGS. 2 a and 2 b are subsequently used to show the implementation ofthe known service feature “call transfer” or “call transfer group” in adirectly communicating communication network, with FIG. 2 a showing theconfiguration of a communication arrangement for implementing theseservice features, while FIG. 2 b shows the connection setup to a memberof a call transfer group.

FIG. 2 a shows the clients B, C, D which are already described in thepreceding descriptions of the figures. Generally, there are variousoptions as to how clients in a communication network can be combined toform a group. By way of example, it is possible to use a (manual)administration operation to determine the members of a group and tonotify each of the clients which are meant to be a member of this groupof this group membership and of the information about the other membersin the group. Another way is to notify each client in a communicationnetwork, by means of a definition, of which properties a client needs tohave in order to be part of a particular group. Each client itself thendecides whether it belongs to this group defined in this manner, andnotifies all other clients in the communication network, for example bymeans of a “broadcast message”, that it belongs to the group. In thepresent exemplary embodiment, clients B and D have already been combinedto form a call transfer group. The text below describes how this calltransfer group is extended by client C (step a).

Clients B, C, D each comprise a database DB, DC, DD which is used tostore group information. In this example, the call transfer group isintended to be administered from the workstation of client B. For thisreason, client B sends client C a configuration message 21 containing agroup identification (group name) and a list with the names and addressinformation of the group members to date. Client C now decides that itneeds to belong to the call transfer group. Therefore, an appropriatedata record recording the names and address information of the clientsB, C, D belonging to the group is created in the database DC. Client Cthen sends a confirmation message 22 to client B, and the latter changesits associated database DB in line with the group extension. Client Bnow sends an information item 23 to each other client in the calltransfer group (in this case client D) which has not yet been informedabout the extension to the call transfer group. When this message 22 hasbeen received, client D now also extends the entries for the calltransfer group in its database DD and then sends an acknowledgementmessage 24 to client B.

Alternatively, the clients may also be programmed such that a new clientC added to the group sends the information about its group membershipitself to the as yet uninformed group members (clients B, D).

The text below uses FIG. 2 b to describe how a call to a member of thecall transfer group formed in the exemplary embodiment shown in FIG. 2 ais made. Unlike in FIG. 2 a, FIG. 2 b also shows client A, which hasalready been introduced as part of the description of the figuresrelating to FIG. 1 a. Client A sends a control message 13 to set up acommunication link to client B. The call is immediately signaled onclient B (client B “rings”); at the same time, client B establishes fromthe information in its database DB that the call needs to be signaled onthe other members of the call transfer group, namely client C and clientD. For this reason, client B sends clients C and D a respectivesignaling call (“multicast message”) 25, 26, which contains firstly thename and the address information of client B as a “sender statement”,and secondly the information that a call waiting on client B can betransferred by client A (step b). While the directly called client B hasthe status (call state) “busy” at the start of call signaling, clients Cand D now signal the call waiting on client B by virtue of theircontinuing to be in the call state “free”.

In the present exemplary embodiment, it is now client C which wishes totransfer the call waiting on client B. To this end, client C sends acall transfer message 27 to client B (step c). Client B now stops thecall signaling, and client B also sends a message 28 to client D inorder to stop signaling the call to client D. In addition, client B nowsends a call diversion message 29, in which client A is now notified ofthe name and the address information of client C. As a result, thecommunication link K2 is now set up to client C by client A (step d).

As already described, as soon as it is called by client A, client Bsends the messages 25 and 26 specifically to the other members of thecall transfer group, namely to client C and client D. Alternatively,however, it is also possible for the called client B to send a“broadcast message”, containing the information about the waiting calland the name of the call transfer group, to all other clients (includingthe ones not shown here) in the communication network. Each client whichreceives this “broadcast message” then uses the information held in themessage to decide whether or not it belongs to this call transfer groupand needs to signal this call waiting on client B for transfer.

In the exemplary embodiment described, it is possible that more than oneof the clients signaling the call wishes to take the call (step c). Inthat case, a plurality of call transfer messages 27 (“call transferrequest”) arrive at the called client B. In this case, only the firstincoming call transfer request is considered, while the other messagesarriving subsequently (“late”) are rejected or answered using a negativeacknowledgement response.

The text below uses FIG. 3 a to show the implementation of the servicefeature “group call” in a directly communicating communication network.The configuration of the group for the group call is effected in asimilar manner to the configuration of the call transfer group,described with reference to FIG. 2 a, and is therefore not explainedfurther at this point (step a).

In the present example, it is assumed that a client A wishes to reach anarbitrary one of the other clients B, C. To this end, client A sends acall message 31 (step b), in the form of a broadcast message, whichcontains the name of the desired group, to all the clients which can bereached in the communication network. This call message 31 is receivedby clients B and C, so that both clients B, C change to the called state(that is to say are in the call state “busy”) and respectively signalthe waiting call from client A. The call is now accepted by one of theclients B, C (in this case by client B), with client B sending a callacceptance message 32 to client A (step C), and with this callacceptance message 32 naturally comprising the address information ofclient B. The communication link K3 between client A and client B isthen set up (step d), and also client A sends a cancellation message 33,in the form of a “broadcast message”, in which completion of theincoming call is confirmed by referring to the previously sent callsignaling message 31, after which the call signaling is terminated inclient C.

As an alternative to the procedure described above, client A may have astored table listing all group members. In this case, the call signalingmessage 31 is not sent in the form of a “broadcast message” to all theclients in the communication network, but rather in the form of a“multicast message” just for the members of the group, that is to say toclient B and client C (step b).

Another variant of the group call is a combination of the previouslydescribed method and the method explained with reference to FIG. 2 b, inwhich client A sends just one call signaling message to one of theclients in the group, and this called client ensures that the call issignaled further to the other members of the group, in a similar mannerto the case of the call transfer group (step b). In contrast to the calltransfer group, however, this call is signaled to all the group membersnot as a call which is to be transferred, but rather as a “full” call,with each client called in this manner changing to the operating states“busy”.

Another variant of the service feature “group call” is the “line group”,in which the members of the group (of the line group) do not signal awaiting call simultaneously but rather in succession in a stipulatedorder. This case is shown in FIG. 3 b.

In a similar manner to the method shown in FIG. 3 a, client A sends acall signaling message 31 in the form of a “broadcast message” to allthe clients B, C in the communication network (step b). The respectivedatabases DB and DC in the clients B and C contain all the groupinformation, with each group member being shown with a separate index inthis table, and each group member having an associated period of timewhich indicates how long a call is to be signaled (“to wait”) on thisrespective client.

The call signaling message 31 is now received by one of the groupmembers, for example by client B. Client B now sends a synchronizationmessage 35 to client C and thus informs client C about the waiting call.Client C acknowledges receipt of this message 35 using anacknowledgement message 37 on client B and, for its part, sends asynchronization message 36 to client D, which in turn sends anacknowledgement message 38 to client C. Client D, as the last groupmember, then sends a final synchronization message 39 to client B, whichsynchronization message is in turn acknowledged on client D by client Busing an acknowledgement message 40. Each synchronization message sentcontains a complete “history” of the previously informed clients. Inaddition, each received acknowledgement message is forwarded from theclient which received this acknowledgement message to its “preceding”client. Furthermore, the clients are programmed such that if a client,for example, client C, is not available then this is registered by thepreceding client (client B) after a waiting time has elapsed, and clientB then sends a new synchronization message to the client with the nexthighest index descriptor, in this case client D. This ensures that evenwhen clients have failed and are absent the synchronization cycle iscompleted and hence after the end of the synchronization cycle all theclients in the group contain the information about the available clientsin the group, and it is thus definite which of the available clients hasthe lowest index number and therefore signals the call first. If thiscall signaled on the client with the lowest index number (in thisexemplary embodiment client B) is not accepted, the client B calledfirst sends an appropriate message to its successor client C (or in thecase of one of the faults described to client D), and itself stopssignaling the call. If the call is now accepted on one of the clients,for example on client D, then client D sends an appropriate message forcall transfer to client B (step c) as in the exemplary embodiment shownin FIG. 2 b, which results in the communication link K4 being set up(step d).

When the call is accepted, a message from client D, which has acceptedthe call, can be sent to the other members of the group so that theindex numbers of the group members are changed in the database DB, DC,DD. This ensures that for the next incoming call the call is signaledfirst on another of the clients. This is important in call centers, forexample, in order to achieve a uniform utilization level or load for thecall center agents.

FIG. 4 shows an alternative illustration of clients A, B, C, with thedirectly communicating communication network IP-N used being acommunication network which interchanges the data on the basis of theInternet protocol (IP network). Clients A, B, C store respective detailsabout their own identity, that is to say their own name, user name,network address etc., and also details about their own functionality(e.g. usable voice codecs, video functionality, maximum bandwidth etc.)(step a). Clients A, B, C also have a respective address database DBA,DBB, DBC which can be used to store the names and address information ofrespective other clients and other information associated with theseclients. These address databases are preferably used as an “electronictelephone book” for setting up communication links. To fill its addressdatabase DBA with information, particularly the address information forother clients, client A sends a “broadcast message”, as a requestmessage, to all the clients which can be reached in the communicationnetwork (step b). The request message contains the information thatclient A wishes to retrieve the address information of other clients. Asa filter criterion, the request message also comprises the informationthat only information about clients which are in the form of amultimedia PC, that is to say have a functionality correspondingthereto, is required. The message is respectively received by client Band client C, which are both in the form of a multimedia PC, so thatthey send a respective response message to client A (step c). Theresponse message respectively contains the client's own name and its ownaddress information and also further information (name of the user,location etc.). These response messages are received and evaluated byclient A, the information contained in the response messages beingrespectively added to the database BDA. At a later time, thisinformation can be retrieved from the database BDA, with client A usingthe respective address information to set up a communication link toclient B or to client C (step d).

The text below uses FIG. 5 to show the “parking” and resumption of a“parked” communication link. FIG. 5 shows a directly communicatingcommunication network containing the clients A, B, C, which correspondto the clients A, B, C from the preceding exemplary embodiments andwhich are therefore not described again. In addition, a special client Wis part of the communication arrangement, said client serving as awaiting destination and being able to receive communication links sothat these communication links from a caller does not need to be broken,for example while a new contact is being sought.

Client A sets up a communication link K5 a to a client B, client A beinga customer, for example, which, as client B, is calling the telephoneexchange in a company or department store. When the user of client B hasreceived information about the desired contact from the caller (clientA), client B sends a request message (51) to the client W used aswaiting destination and in so doing requests the index number of a freepark position. Client W sends client B the required park position number(e.g. “22”) (step a); this park position number “22” is displayed on thedisplay of client B. Client B now uses a message (52) to send client Athe address information of client W, and asks client A from now on tocontinue the communication link K5 a not with client B, but rather as acommunication link K5 b with client W. Subsequently, the communicationlink K5 b between client A and client W has thus been set up, withclient W sending client A waiting music or—in the case of multimediaclients—any desired multimedia contents for information andentertainment purposes. The user of client B now uses a message (53) tocall the connection of a “paging installation” P in order to make anannouncement (54) in the building (company; department store) whichrelates to the desired person and which comprises the park positionnumber, that is to say for example “Herr Muller, 22 please”. The personcalled in this way now goes to the next available client, client C, andactivates a function on this client C in order to transfer parkedcommunication links.

Since, in a larger communication network, a multiplicity of clients maybe provided with position stores for waiting purposes, client C nowsends a search message (55) (step b), in the form of a broadcastmessage, which contains the park position number 22 previously input bythe sought person, to all the clients in the communication network.While clients A and B cannot allocate a park position number “22”,client W responds to the search query (55) with a response message (56)which comprises not only the confirmation but also the addressinformation of client W (step c). In addition, client W uses a diversionmessage (58) to notify client A that the existing communication link nowneeds to be continued with client C as the communication partner, as aresult of which the call (the communication link K5 b) is forwarded suchthat the communication link K5 c (the useful data channels) are from nowon connected between client A and client C (step d).

Instead of the multimedia PCs described, the examples can also use lesspowerful terminals which are not set up to execute the steps described,for example sending “broadcast messages”. Such terminals can have thesesteps executed by other clients, which execute the stepsrepresentatively as “proxies”. In this case, particular methods andfunctions can also be executed by arranging specialized proxies in anetwork which are able to be found by the clients for use, for exampleusing search messages.

1. A method for setting up a communication link between a plurality ofclients in a communication network, comprising: storing client addressinformation in a distributed form for the plurality of clients;establishing a waiting communication link between a sought client and awaiting destination client; the waiting, destination client sending awaiting destination descriptor; transmitting a broadcast request messagefrom a searching client; the waiting destination client sending aresponse message comprising a client address information to thesearching client; and the waiting destination client sending signalinginformation configured for setting up the communication link between thesearching client and the sought client.
 2. The method according to claim1 wherein the client address information is stored in at least onedatabase.
 3. The method according to claim 2, wherein the stored clientaddress information describe clients in a call transfer group, whereinthe broadcast message is transmitted to the call transfer group clientsdescribed in the stored client address information, and wherein theclients involved in the communication link are in a free operating stateat a start of the sending of signaling information.
 4. The methodaccording to claim 1 wherein the signaling information is rejected ornot answered within a time period by the sought client; and wherein thebroadcasted message includes an identifier for the sought client, andwherein the client address information in the response message is for acall diversion client.
 5. The method according to claim 1 wherein thesignaling information is sent in a diversion message.
 6. The methodaccording to claim 5, wherein the response message is comprised of aclient address information item.
 7. The method according to claim 1wherein the searching client belongs to a call transfer group, and themethod further comprising transferring the waiting communication link tothe searching client using the stored client address information thatdescribes clients in the call transfer group.
 8. The method according toclaim 1 wherein the communication link is formed from transferring thewaiting communication link to the searching client via the waitingdestination client.
 9. The method according to claim 8, wherein thesought client is a client in a call transfer group, wherein the clientaddress information in the response message is for the sought client,and wherein the communication link is set up between the searchingclient and the sought client.
 10. The method according to claim 1wherein the stored client address information describe clients in agroup.
 11. The method according to claim 1 wherein the communicationnetwork is a directly communicating communication network.
 12. Themethod according to claim 11, wherein the waiting destination descriptoris sent to the searching client.
 13. The method according to claim 11,wherein the sending of signaling information is effected by the sendingof the response message to the searching client.
 14. The methodaccording to claim 1 wherein the client address information in theresponse message is stored by the searching client in a database, andwherein the database is accessed to set up the communication link. 15.The method according to claim 1 wherein the broadcast message comprisesat least one filter criterion for selecting particular clients, andwherein the waiting destination client meets the at least one filtercriterion.
 16. The method according to claim 1 wherein the broadcastmessage comprises at least on filter criterion for selecting particularclients, and wherein the waiting destination client has a property thatmeets the at least on filter criterion.